With the inclusion of the 'Predatory fighters' - rule, are unit champions now more viable? I used to leave them out and simply add another body for combat ress.
You're paying 10 points for an additional attack, that comes with a 1 in 6 chance of an additional attack. That isn't in for me - i'd rather use 10 points elsewhere.
It really depends on what you're using the unit for. If your saurus are just going to be an anvil, that sits there soaking up damage, a champion comes in handy against any big nasty heroes or lords. You can challenge them out, and for that first round of combat you know you are only losing one model, helping to preserve your unit's size. While you can almost buy another saurus warrior for the same points, by challenging out a horrible character you can easily preserve an additional 3-4 models in that first round. They also lose out on their Thunderstomps, if they have any, for that round, and so to me champs are always worth it on infantry blocks that you intend to preserve the size of.
What? You don't want to hold up that rampaging Daemon Prince for another turn? Well, okay then I guess... More seriously, I never used to bother with unit champions either. Then one of my group started collected Warriors of Chaos - this was back in the old book - and the other started running his High Elf Prince on a Dragon. Then, like Canegham said, having something which can basically defuse them for one turn became worth its wait in gold.
Besides tying up an enemy beat stick, you can also soak a challenge to leave your own beatstick(s) swinging on rank and file. Unit champs score you a bonus 50 points if they kill a character in a challenge.
Meaning Kroxigor Ancients are a bargain since they are more likely to beat a character in a challenge than any other champion we can field.